iio_readdev: Use sigwait instead of sigwaitinfo
iio_readdev: Use sigwait instead of sigwaitinfo

They are basically the same, but the latter is not available on OSX.

Signed-off-by: Paul Cercueil <73d292422978d45c9eeef455bb1b24a0db453722@analog.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio